1. Field of the Invention
The field of this invention is earth boring bits--especially the seal and lubrication systems for rolling cutter rock bits.
2. Description of the Prior Art
Recently, metal face seals have been used successfully to seal lubricant within the rotatable cutters and around the cantilevered bearing shafts of a rock bit. U.S. Pat. No. 4,516,641, "Earth Boring Bit With Pressure Compensating Rigid Face Seal", May 14, 1985, includes background information leading to this milestone in the continuing search for seal improvement. The seal disclosed in U.S. Pat. No. 4,516,641 utilizes two rigid rings which are urged against one another by a pair of elastomeric rings confined in a seal groove between each cutter and its supporting bearing shaft. Since the axial seal assembly movement is greater than axial cutter movement, a groove geometry is provided to permit unrestricted seal assembly movement. As a result, pressure pulses in the lubricant around the seal and lubricant losses are minimized. The seal assembly becomes a supplemental pressure compensator that assists the primary compensator in each leg of the bit in maintaining a selected low pressure differential across the seal assembly.
An improvement to the structure disclosed in U.S. Pat. No. 4,516,641 is disclosed in U.S. Pat. No. 4,666,001, "Earth Boring Bit With Improved Rigid Face Seal Assembly", May 19, 1987. If the rigid rings are positioned in a groove inside the periphery of an associated journal bearing surface, axial seal movement may be decreased relative to axial cutter movement. In the preferred embodiment axial seal assembly movement is one half that of the cutter, which better balances the loads applied to each half of the seal assembly. Hence, prolonged life of the seal assembly may be expected.
Each of the seal assemblies disclosed in the above patents uses two opposed rigid rings and two resilient energizer rings in a groove configuration to achieve lubricant pressure equalization in the vicinity of the seal. It would be advantageous to achieve the results of these seal assemblies with fewer components in a reduced space. This would simplify manufacture, foreseeably reduce costs, and enable utilization in a wider variety of bit sizes and maybe even bit types.